1. Technical Field
The present invention relates to stationary blades used in a steam turbine, and, more specifically, it relates to an internal structure of stationary blades and a steam turbine including the stationary blades having such an internal structure.
2. Description of the Related Art
In recent years, in order to reduce the weight of steam turbines, a technique for forming cavities in stationary blades, i.e., a hollow structure, has been known. Furthermore, in order to improve the performance, a technique has been proposed in which slits communicating between cavities of stationary blades and the outside are provided to introduce water droplets deposited on the surface of the stationary blades into the cavities to remove them (for example, see Japanese Unexamined Patent Application, Publication No. Hei 11-336503). The water taken into the cavities flows toward a shroud bonded to the stationary blades and is discharged therefrom.
Such steam turbine stationary blades sometimes cause self-excited vibrations (flutter) depending on the exterior shape (geometrical shape) and mass thereof and the environment around the stationary blades (for example, the flow rate and mass of the steam passing through the stationary blades) while the turbine is operated. In particular, it is known that the self-excited vibrations tend to occur when the mass of the stationary blades is small and when the blade width (the entire length of the blades) is large.
To reduce such self-excited vibrations, a technique for attenuating vibrations occurring at the stationary blades by providing attenuation mechanisms (dampers) at bonding portions of the stationary blades and the shroud has been proposed (for example, see Japanese Patent No. 3461562 and Japanese Patent No. 2877837).